The number of chronically hungry people has surpassed the 1bn mark for the first time as the economic crisis compounds the impact of high food prices, the United Nations’ top agriculture official has warned.

In an interview with the Financial Times, Jacques Diouf, director-general of the Food and Agriculture Organisation, warned that the increasing numbers of undernourished people could trigger political instability in developing countries.

“The issue of world food security is an issue of peace and national security,” he said, urging world leaders who are discussing ways to resolve the economic crisis not to forget that last year more than 30 countries suffered food riots.

The Rome-based organisation estimated last year that about 960m people were chronically hungry in 2008. Mr Diouf said that had since risen and “unfortunately, we are already quoting a number of 1bn people on average for this year”.

Before the food crisis started in 2007, there were less than 850m chronically hungry people in the world, a level that has been roughly constant since the early 1990s owing to the global fight against poverty and countries such as China lifting their economic growth.

Mr Diouf’s assessment signals that the food and economic crisis have reversed the past quarter-century’s slow but constant decline in the proportion of undernourished people as a percentage of the developing world’s population.

The percentage fell from 20 per cent in 1990-92 to a low of just below 16 per cent in the 2003-05 period. But with 1bn people chronically hungry now, the percentage has risen to almost 18 per cent.

As a consequence, the FAO’s director-general proposed ditching the UN’s Millennium Development Goal of halving the number of the world’s undernourished by 2015 and replacing it with a target of “eradicating hunger by 2025”. He said to meet that aim, the world should learn from the mistakes of the 1990s, when investment in agriculture fell sharply, paving the way for the surge in food prices of the past two and a half years.

Mr Diouf is pressing world leaders for a summit in Rome in November to tackle the roots of food insecurity, rather than to continue reacting to every crisis with ad hoc measures. “The food crisis is not over,” he said, warning that although international benchmark prices for major agricultural commodities such as wheat, corn, rice and soyabean had fallen from last year’s peak, they remained almost 30 per cent above the 2005 level. He added that domestic prices in developing countries had not tracked the drop in international prices as their crops had been disappointing.

Now, he said, “the financial crisis is worsening the situation by increasing unemployment, limiting the credit for trading [agricultural commodities] and lowering remittances, which in poor countries were used to purchase food”.

“Combining all the elements we are in a very unstable situation,” he added.

At the proposed summit, Mr Diouf said that world leaders should commit to investing in agriculture, particularly in the developing world, as the rise in the world’s population from today’s 6.5bn people to 9bn by 2050 will mean the world needs to double its current food output.

He added that leaders also should agree to revive the FAO’s Committee on World Food Security, elevating it to ministerial level to “allow policy decisions [to] be made”.

Mr Diouf said that several heads of state and governments already back its idea of a summit in November to tackle the food problem. Previous summits, however, have yielded few policy results.